This invention relates to continuous casting apparatuses and methods.
Continuous casting of metals and metal alloys of various kinds, both ferrous and nonferrous, has been undertaken for many years. The majority of the prior art discloses machines in which casting is performed by discharging molten metal between a pair of rollers which are continually cooled. It is possible to cast vertically downward, downward at an angle, or horizontally.
Continuous casting of metals is undertaken by two common methods that are similar in some respects. Briefly, continuous casting is performed by means of endless members e.g. mold blocks mounted on or forming continuous chains, or endless belts with moving side dams disposed between the belts. The endless members which are typically disposed horizontally or slanted at a small angle from the horizontal serve as the mold for the cast metal, e.g., billet, slab, sheet, plate, or strip. The endless members, moving in non-circular paths, come together tangentially in a casting region to form a casting mold channel and stay together long enough so that the metal is solidified enough to support itself after which the endless members separate and are carried back to the beginning of the casting region. This method of casting has proved efficient and economical particularly in the casting of shapes such as slab, plate or strip, which may be used as the finished product, or if desired, the shape may be subjected to reduction rolling as it emerges from the horizontally disposed casting machine.
As stated, these generally horizontally disposed continuous casting machines are predominantly of two types. The first type utilizes a pair of continuous belts which approach each other tangentially to form a movable mold therebetween. As the molten metal is introduced between the belts, the belt is cooled. The cooling is, however, somewhat inefficient, and the thickness of the strip varies because of the lack of stiffness in the belt. To prevent variations in the thickness and shape of the strip, the molten metal must be supplied to the mold at a low pressure which effects the casting process and causes surface and shape problems as well as deficiencies in the metal structure.
To overcome the inefficiencies in cooling, thickness, and cast metal quality control, the belt is replaced with a continuous chain in the second type of caster which has consecutive mold blocks attached to or actually forming the chain. The mold blocks provide a structure which can be externally cooled, internally cooled, or both externally and internally cooled. This structure efficiently cools the metal being molded between the caster blocks, and the continuous caster utilizing the mold blocks also provides increased stiffness which results in a uniform thickness of the strip. This process is, however, subject to other deficiencies. Where the consecutive mold blocks abut each other, molten metal can flow in between the blocks and solidify there creating protrusions extending from the molded metal across its width. These protrusions are commonly referred to as fins. The presence of fins on the molded strip interferes with the subsequent formation processes, such as rolling, to which the molded metal might be subjected.
Further, it is frequently necessary, during the casting of flat products such as sheets or strips, to adjust the width of the strip. To adjust the width of the strip, different widths of chains must be kept in stock or continuous, expensive, adjustable width side dams which are movable across the width of the blocks must be provided. Because of the weight and bulk of the chain, the change is a difficult, time consuming, and extremely costly procedure.
It has also been difficult to obtain high accuracies of strip thickness/shape with the continuous casting machines. As the molten metal moves along the length of the chain caster, the metal cools and solidifies in the mold channel. As the metal cools, the volume decreases thus changing the casting pressure applied to the metal as it solidifies in the mold channel. The metal may even lose contact with the mold channel. This slows cooling thus requiring a longer mold channel, and under some circumstances, this can lead to undesirable variations in thickness and other shape deformations. More frequently, this has adverse effects on the microstructure of the cast product.
Thus, the production of continuous cast products without fins is desirable to enhance the products fabricated from continuous casting process and increase the ability to subject the continuously cast metal to further processing. It is also desirable to change the mold width of a continuous caster utilizing a chain without changing the chain. Further, it is desirable to maintain the casting pressure on the metal as it solidifies. The production of continuous cast products without fins, shortening the stop time of a width change, changing the mold width without changing the chain, and controlling the casting pressure, translate directly into increased use of continuously cast products and a reduction of manufacturing expenses for continuously cast products.